The invention relates to a method for propulsion of water-going vessels by means of a body which can be moved forward and backward relative to the vessels hull and which has a propulsion portion which is located in the water, a drive device which is arranged to move the body in a first direction, and a first resiliently elastic device or spring device which is arranged to exert spring forces against and move the body in a second, opposite direction, the propulsion portion""s water resistance being greater when it is moved opposite a desired propulsion direction for the vessel than when it is moved in this propulsion direction.
The invention also relates to a device for performing the method.
In FR-A-2 446 220 there is disclosed a device of this type, However, there is no suggestion as to second spring means acting in the active direction of the propelling body such as to form an oscillating system with the propelling body and the first spring means in two directions about a neutral position and to provide for sinusoidal variation of the motive power.
In known types of mechanical propulsion of vessels where a body is moved in water which surrounds the vessel in order to provide a flow of water in a direction which is oppositely directed to the desired motion of the vessel, the body is rotated. Thereby relative movements of the water and the body are created and associated components of the force which are exerted by the water on the body, where some of these components do not contribute of the propulsion of the vessel. This is the case, e.g., in propeller propulsion as well as paddle wheel propulsion.
For propulsion of this kind where a mass of water m with a velocity v, e.g., is thrust backwards from a vessel per time unit, a reaction force F=m xc2x7v is obtained. Since the space available for a propeller behind a vessel is limited, and the propeller only partly utilises this space, a relatively high velocity v must be selected in order to achieve an acceptable thrust. This results in a substantial power loss as a result of propeller resistance, eddying, etc., in addition to possible cavitation.
The object of the invention is to provide a method and a device of the type mentioned in the introduction, which is not encumbered by these disadvantages.
The characteristics of the method and the device are described briefly as follows.
A method for propulsion of water-going vessels by means of a body (8, 9, 10) which can be moved forward and backward relative to the vessel""s hull in accordance with the principles of the claimed invention has a propulsion portion (9) which is located in the water (2), a drive device (4) which is arranged to move the body (8, 9, 10) in a first direction, and a first resiliently elastic device or spring device (11) which is arranged to exert spring forces against and move the body (8, 9, 10) in a second, opposite direction. The propulsion portion""s (9) water resistance is greater when it is moved opposite a desired propulsion direction for the vessel than when it is moved in this propulsion direction.
The body (8, 9, 10) is influenced by further spring forces which are exerted in the first direction. The amount of motive power is varied sinusoidally. The spring force-influenced body (8, 9, 10) is brought into translatory and rectilinear oscillation with a natural frequency (E) in the two directions about a neutral position (N2), the neutral position (N2) being determined by a static equilibrium between the spring forces influencing the body (8, 9, 10).
A device for propulsion of water-going vessels by means of a body (8, 9, 10) which can be moved forward and backward relative to the vessel""s hull in accordance with the principles of the claimed invention has a propulsion portion (9) which is located in the water (2), a drive device (4)which is arranged to move the body (8, 9, 10) in a first direction, and a first resiliently elastic device or spring device (11) which is arranged to move the body. (8,9,10) in a second, opposite direction. The propulsion portion""s (9) water resistance being greater When it is moved opposite a desired propulsion direction for vessel than when it is moved in this propulsion direction.
The device comprises a second resiliently elastic device or spring device (12) which is arranged to move the body (8, 9, 10) in the first direction. The spring devices (11,12) and the body (8, 9, 10) forin-an-oscillating device with a natural frequency (E). The drive device (4) is arranged to provide the oscillating device with sufficient energy to bring the body (8, 9, 10) into oscillation with a natural frequency (E) and with a desired amplitude.